图、DFS 与 BFS

def dfs(node):
  if node in visited: return
  visited.add(node)
  for neighbor in graph[node]: dfs(neighbor)

for each cell:
  if is_new_component(cell):
    answer += 1
    flood_fill(cell)

queue = all_zero_indegree_nodes
while queue:
  node = pop()
  for next in graph[node]:
    indegree[next] -= 1
    if indegree[next] == 0: push(next)

dist[start] = 0
heap = [(0, start)]
while heap:
  d, node = pop_min()
  if d != dist[node]: continue
  for next, weight in graph[node]: relax()